1. Field of the Invention
The present invention relates to a filter unit, duplexer, and communication apparatus for use in microwave frequency bands, for example.
2. Description of the Related Art
Up to now, filter units which allow two or more frequency bands to pass through at the same time have been composed of two or more bandpass filter units electrically connected in parallel. For example, in the case of a filter unit 91 allowing two frequency bands fa and fb to pass through simultaneously as shown in FIG. 13, a bandpass filter unit F21 allowing a frequency band fa to pass through and a bandpass filter unit F22 allowing a frequency band fb to pass through are electrically connected in parallel. FIG. 14 shows a filtering characteristic curve of the filter unit obtained in this way.
However, in the prior art filter unit, it is required to connect electrically in parallel the same number of bandpass filter units as the number of frequency bands to be allowed to pass through. Therefore, as the number of frequency bands to be allowed to pass through increases, the number of bandpass filter units connected in parallel increases. Because of this, the filter unit becomes large-sized and the soldering work for mounting the bandpass filter units, and so on, increases, and accordingly there is the problem that the manufacturing cost of the filter unit increases.
To overcome the above described problems, embodiments of the present invention provide a filter unit, a duplexer, and a communication apparatus which are small-sized and of low manufacturing cost.
One embodiment of the present invention provides a filter unit comprising: a wideband bandpass filter; at least one band-elimination filter having a stop band within the passband of the bandpass filter, the passband being divided into a plurality of pass bands by the stop band; and the wideband bandpass filter and the band-elimination filter being disposed in a single dielectric member.
In the above described filter, the bandpass filter and band-elimination filter may comprise at least one dielectric filter.
In the above described filter, the bandpass filter and band-elimination filter may comprise at least one strip line filter.
Another embodiment of the present invention provides a duplexer comprising at least one of above described filters.
Yet another embodiment of the present invention provides a communication apparatus comprising at least one of the above described filter or the above described duplexer.
According to the above described structure and arrangements, the passband of a bandpass filter is divided into a plurality of pass bands by the respective stop bands of one or more band-elimination filters. Thus, the signals having frequencies corresponding to these divided pass bands are able to pass through simultaneously.
Further, a duplexer and a communication apparatus according to the present invention are made small-sized because they are made up of a filter unit having the above characteristics.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.